docs: add Fluent Theme to docs

Author: ghiscoding

frameworks/slickgrid-react/docs/styling/styling.md

@@ -32,6 +32,7 @@ The Material & Salesforce Themes are using SVGs internally for the icons used by
 @use '@slickgrid-universal/common/dist/styles/css/slickgrid-theme-bootstrap.css';
 @use '@slickgrid-universal/common/dist/styles/styles/css/slickgrid-theme-material.css';
 @use '@slickgrid-universal/common/dist/styles/css/slickgrid-theme-salesforce.css';
+@use '@slickgrid-universal/common/dist/styles/css/slickgrid-theme-fluent.css';
 ```
 
 ##### with SASS
@@ -44,8 +45,10 @@ The Material & Salesforce Themes are using SVGs internally for the icons used by
 );
 
 // or other Themes
+@use '@slickgrid-universal/common/dist/styles/sass/slickgrid-theme-bootstrap.scss';
 @use '@slickgrid-universal/common/dist/styles/sass/slickgrid-theme-material.scss';
 @use '@slickgrid-universal/common/dist/styles/sass/slickgrid-theme-salesforce.scss';
+@use '@slickgrid-universal/common/dist/styles/sass/slickgrid-theme-fluent.scss';
 ```
 
 ### Using CSS Variables _(instead of SASS)_